What is the role of detrusor overactivity in urge urinary incontinence pathophysiology?

Updated: Sep 23, 2019
  • Author: Sandip P Vasavada, MD; Chief Editor: Edward David Kim, MD, FACS  more...
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Answer

Mills and colleagues conducted a comparison study of bladder muscle strips from patients with severe idiopathic detrusor overactivity and from organ donors with no known urologic problems. [16] The following are some of the findings:

  • Patchy partial denervation of the detrusor with areas of normal innervation and areas of reduced innervation by fibers staining for acetylcholinesterase

  • A reduced force of contraction in response to electrical field stimulation: This finding is in contrast to a previous study showing an increased sensitivity to electrical field stimulation, but the authors believe that the muscle strips may have had increased sensitivity to direct electrical stimulation (non–nerve mediated).

  • Supersensitivity to potassium

  • Increased electrical coupling of cells via cell-to-cell junctions

  • Variability in the activity of muscle strips from the same bladder

The authors believe that the primary abnormality in detrusor overactivity is at the detrusor muscle level with an increased capacity for spontaneous myogenic contractile activity and spread of electrical activity from cell to cell, resulting in tetanic contractions. Epidemiological studies have shown an association between detrusor overactivity and irritable bowel syndrome. [19] Some authorities have proposed that a syndrome of smooth muscle dysfunction may underlie this association.

Another study demonstrated the presence of an increased ratio of abnormal-to-normal cell junctions in patients with bladder dysfunction. The increased ratio was demonstrated most markedly in patients with detrusor overactivity. To a lesser degree, these changes also were observed in patients with outlet obstruction combined with detrusor overactivity and with idiopathic sensory urgency alone. [20]

These authors concluded that idiopathic sensory urgency might represent a milder or less overt variant of detrusor overactivity. They suggested that, in the future, bladder biopsy with structural evaluation of cell junctions might become a useful clinical tool in the diagnostic evaluation of bladder dysfunction. [20]

One study proposed that urge incontinence, regardless of the triggering mechanism, may share a final common pathway of myogenic dysfunction of the detrusor. [21] Spread of contractile signals via cell-to-cell coupling was proposed as the likely mechanism.

Another possible explanation for detrusor overactivity in a subgroup of patients involves the triggering of the micturition reflex by leakage of urine into a funneled and partially incompetent proximal urethra. This theory is consistent with the findings of detrusor overactivity caused by coughing or changing position.


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